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Replacement blade tension spring for Powermatic 20" bandsaws - what size?

richard newman

Titanium
Joined
Jul 28, 2006
Location
rochester, ny
The blade tensioning spring on my 20" Powermatic 81 and 87 bandsaws are entirely inadequate. Have to compress them completely and then crank some more to get up to 25,000 psi on a 1/2" x .025" blade, measured with a Starrett tension gauge.

Doing the math for a 1/2" x .035" blade at 25Kpsi, I get 438 lbs (ignoring the gullet width). Doubling that, as its a loop rather than a single strand of blade = about 876 lbs. Seems like the spring max load should be significantly higher to allow for fatigue and a safety margin, maybe 1000, 1500 ...? I'm thinking die springs from McMaster. The saws are welded frames, pretty flexible compared to cast iron, but capable enuf for my needs

Anyone done this? Is my thinking reasonable?
 








 
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